[Elecraft] KX1: 40M low power, 20 not working on transmit

[John Donovan]

Hey Don,

That fixed it, thanks!! I had the wrong value for C52--close, but no 
cigar. Now to do final assembly, work a few contacts, then build the 
antenna tuner. Happy, happy!

73,
John K6YLG

On 9/4/2011 4:19 PM, Don Wilhelm wrote:
> John,
>
> Sorry that I could not help before the Labor Day weekend, but the 
> Shelby Hamfest called and I just arrived back home.
>
> While the change on RF voltage on Q4's base between transmit and 
> receive may appear disconcerting, it may or may not be the problem.  
> The DDS operates 4913 kHz lower than 14 MHz during receive, or 4913 
> kHz higher than the RX frequency when on 40 meters, while during TX, 
> the DDS frequency is shifted to the TX output frequency.
>
> It is wise to check and double-check the 14 MHz Low Pass Filter 
> following the DDS for correct values and good soldering.  L4. L5, C50. 
> C51, and C52.
>
> 1.2 volts on the source of Q1 is normal.
>
> Once you have solved the lack of output from the DDS LPF on 20 meters, 
> you can move on to the PA LPF.  Count the turns on L1 and L2 (count 
> the number of times the wire passes through the center of the core), 
> and check the capacitors for correct values.
>
> 73,
> Don W3FPR
>
> On 9/3/2011 12:19 PM, John Donovan wrote:
>> I just finished building my KX1 and the receiver works great. I get 2W
>> out on 40 but nothing measurable on 20.   The odd thing is in receive on
>> the base of Q4 I get 2x the signal on 20 that I do on 40; OTOH when I go
>> into TUNE mode that signal ramps way up on 40 but remains insignificant
>> on 20; by the collector of Q5 it's barely there. I checked the voltages
>> on Q1/4/5/6 and they're OK, except that the source of Q1 is only 1.2V. I
>> checked solder joints and they all seem fine; ditto inductors, though T1
>> looks to be a tricky bit of work.
>>
>> Any suggestions would be greatly appreciated. I'd hoped to take this rig
>> camping with me this Labor Day weekend, but it doesn't look like that's
>> going to happen.
>>
>> 73,
>> John K6YLG
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>